(1) Field of the Invention
This invention relates to a substrate treating apparatus and method for performing a predetermined treatment such as etching or cleaning of semiconductor wafers, glass substrates for liquid crystal displays and so on (hereinafter referred to simply as substrates). More particularly, the invention relates to a technique for performing treatment while changing liquids.
(2) Description of the Related Art
Conventionally, this type of apparatus includes a treating tank for storing a treating liquid and immersing substrates therein, a treating liquid supply unit for supplying the treating liquid to the treating tank, and a treating liquid discharge unit for discharging the treating liquid from the treating tank (see Japanese Unexamined Patent Publication No. 2001-23952, for example).
Where, for instance, substrates are made of silicon, silicon concentration in the treating liquid increases with progress of treatment of the substrates with the treating liquid, which gradually lowers a treatment rate. Thus, a “partial liquid replacement” is carried out at a time when a certain number of substrates have been treated, to discharge part of the treating liquid from the treating liquid discharge unit and supply the treating liquid in an amount corresponding to the discharged treating liquid. This partial liquid replacement allows the lowered treatment rate to remain within a certain target range. In this case, a parameter called “life count” set in advance is used to indicate the certain number of substrates. The number (or the number of lots) of treated substrates is counted and, when the count reaches the life count, a partial liquid replacement is carried out.
The conventional apparatus with the above construction, however, has the following problem.
A first treating liquid not having treated substrates and a treating liquid having treated a certain number of substrates are controlled with a common parameter or the life count. In addition, an initial treatment rate is higher than a treatment rate after a partial liquid replacement. As a result, the first treating liquid may be partially replaced before the treatment rate lowers to a certain target range, and thus treatment will be continued without the treatment rate reaching the target range even with a subsequent partial liquid replacement, which may cause a problem that an unsuitable treatment of the substrates is performed.